As described in German patent document 4,110,720 a driven part of a tool is fixed on a drive part of a drive spindle rotatable about an axis by a mount having a tubular extension projecting axially forward from one of the parts and formed centered on the axis with a radially inwardly projecting collar and a recess that is formed on the other part and that is complementarily engageable axially over the tubular extension. A retaining element in the tubular extension has a plurality of dogs deflectable radially between an outer blocking position axially behind the collar and an inner position radially inward of the collar. An actuating member in the retaining element in the tubular extension has a camming edge engageable outward with the dogs and interengaging formations between the actuating member and the other part inhibiting rotation of the actuating member relative to the other part while permitting axial displacement of the actuating member relative to the parts between a rear freeing position clear of the dogs with same in the respective inner position and a front position pressing the dogs outward into the respective outer blocking position.
A ring gear axially fixed in the other part coaxially surrounds the actuating member and is formed with an internal thread meshing with an external thread of the actuating member. A pinion rotatable in the other part about an axis extending radially of the spindle axis has teeth meshing like a right-angle drive with teeth of the ring gear. Thus rotation of the pinion in one direction rotates the ring gear in one direction and displaces the actuating member axially in one direction, and opposite rotation oppositely displaces all these parts. Hence the pinion can be used to axially displace the actuating member and thereby move the dogs between their outer position in which they hold the two parts together and their rear position.
This mechanism is fairly complex and adds excessively to the cost of the tool mount and spindle. In addition it creates an eccentric mass that must be compensated for carefully in order to avoid vibration at high rotation speeds. Unless all the parts are manufactured to very tight tolerances the system can jam or when clamped can exert nonequal force around the perimeter of the retaining element.